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VCE 12 Methods 2023

3.07 Graphical method for trigonometric equations

Worksheet
Solve trigonometric equations graphically
1

Consider the function y = 3 \sin x and the line y = 3 which are graphed below:

-\frac{3}{2}π
-1π
-\frac{1}{2}π
\frac{1}{2}π
\frac{3}{2}π
x
-3
-2
-1
1
2
3
y

State all solutions to the equation 3 \sin x = 3 over the domain \left[ - 2 \pi , 2 \pi\right].

2
a

Graph the function y = \tan x and the line y = 1 on the same number plane over the domain \left[ - 2 \pi , 2 \pi\right].

b

Hence, state all solutions to the equation \tan x = 1 over the domain \left[ - 2 \pi , 2 \pi\right].

3

Consider the graph of y = \cos x over the domain [0, 2 \pi ]:

\frac{1}{6}π
\frac{1}{3}π
\frac{1}{2}π
\frac{2}{3}π
\frac{5}{6}π
\frac{7}{6}π
\frac{4}{3}π
\frac{3}{2}π
\frac{5}{3}π
\frac{11}{6}π
x
-1.5
-1
-0.5
0.5
1
1.5
y
a

State the x-values for which \cos x = 0.

b

State the first x-value for which \cos x = 0.5

c

For what other value of x shown on the graph, does \cos x = 0.5?

d

For what values of x does \cos x = - 0.5?

4

Consider the graph of y = \tan x:

\frac{1}{4}π
\frac{1}{2}π
\frac{3}{4}π
\frac{5}{4}π
\frac{3}{2}π
\frac{7}{4}π
x
-3
-2
-1
1
2
3
y
a

How long is one period of the graph?

b

State the x-values for which \tan x = 0, from x = 0 to x = 2 \pi inclusive.

c

State the first x-value for which \tan x = 1.

d

For what other value of x shown on the graph does \tan x = 1?

e

For what values of x shown on the graph does \tan x = - 1?

5

Consider the function y = \cos \left(\dfrac{x}{4}\right).

a

Sketch the graph of this function over the domain [-4 \pi, 4\pi].

b

Sketch the line y = - 0.5 on the same number plane.

c

Hence, state all solutions to the equation \cos \left(\dfrac{x}{4}\right) = - 0.5 over the domain \left[ - 4 \pi , 4 \pi\right] in exact form.

6

Consider the function y = \tan \left(x - \dfrac{\pi}{4}\right).

a

Sketch the graph of the function for -2\pi \leq x \leq 2\pi.

b

Sketch the line y = 1 on the same number plane.

c

Hence, state all solutions to the equation \tan \left(x - \dfrac{\pi}{4}\right) = 1 over the domain \left[ - 2 \pi , 2 \pi\right). Give your answers as exact values.

7

Consider the function y = 3 \cos 2 x + 1.

a

Sketch the graph of the function for -\pi \leq x \leq \pi.

b

State the other function you would add to the graph in order to solve the equation 3 \cos 2 x + 1 = \dfrac{5}{2}.

c

Sketch the graph of this function on the same number plane.

d

Hence, state all solutions to the equation 3 \cos 2 x + 1 = \dfrac{5}{2} over the domain \left[ - \pi , \pi\right]. Give your answers as exact values.

8

Consider the function y = \sin \left(x - \dfrac{\pi}{3}\right) + 5.

a

Sketch the function y = \sin \left(x - \dfrac{\pi}{3}\right) + 5 over the domain [- 2 \pi, 2 \pi].

b

Sketch the line y = \dfrac{11}{2} on your graph.

c

Hence, state all solutions to the equation \sin \left(x - \dfrac{\pi}{3}\right) + 5 = \dfrac{11}{2} over the domain \left[ - 2 \pi , 2 \pi\right). Give your answers in exact form.

9

Consider the equation 3 \sin \left( 3 x + \dfrac{\pi}{7}\right) = - \dfrac{11}{10}.

a

Which function would be graphed along with y = - \dfrac{11}{10} in order to solve the equation graphically?

b

Graph both of these functions using the graphing facility of your calculator. Hence state all solutions to the equation over the domain \left[ - \dfrac{13\pi}{42}, \dfrac{5\pi}{14}\right]. Round your answers correct to three decimal places.

10

Consider the equation - 5 \cos \left(\dfrac{x}{2} + \dfrac{\pi}{5}\right) = - \dfrac{17}{10}.

a

Which function would be graphed along with y = - \dfrac{17}{10} in order to solve the equation graphically?

b

Graph both of these functions using the graphing facility of your calculator. Hence state all solutions to the equation over the domain \left[ - \dfrac{7 \pi}{5} , \dfrac{13 \pi}{5}\right]. Round your answers correct to three decimal places.

Equations of trigonometric functions from graphs
11

Determine the equation of the graphed function given that it is of the form y = \cos \left(x - c\right), where c is the least positive value.

\frac{1}{6}π
\frac{1}{3}π
\frac{1}{2}π
\frac{2}{3}π
\frac{5}{6}π
\frac{7}{6}π
\frac{4}{3}π
\frac{3}{2}π
\frac{5}{3}π
\frac{11}{6}π
x
-1
1
y
12

Determine the equation of the graphed function given that it is of the form y = \sin \left(x - c\right), where c is the least positive value.

\frac{1}{6}π
\frac{1}{3}π
\frac{1}{2}π
\frac{2}{3}π
\frac{5}{6}π
\frac{7}{6}π
\frac{4}{3}π
\frac{3}{2}π
\frac{5}{3}π
\frac{11}{6}π
x
-1
1
y
13

Determine the equation of the graphed function given that it is of the form \\ y = \sin \left(x + c\right) + d, where c is the least positive value and x is in radians.

-\frac{7}{4}π
-\frac{3}{2}π
-\frac{5}{4}π
-1π
-\frac{3}{4}π
-\frac{1}{2}π
-\frac{1}{4}π
\frac{1}{4}π
\frac{1}{2}π
\frac{3}{4}π
\frac{5}{4}π
\frac{3}{2}π
\frac{7}{4}π
x
-1
1
2
3
4
y
14

Determine the equation of the graphed function given that it is of the form y = a \cos \left(x - c\right), where c is the least positive value and x is in radians.

-1π
-\frac{3}{4}π
-\frac{1}{2}π
-\frac{1}{4}π
\frac{1}{4}π
\frac{1}{2}π
\frac{3}{4}π
\frac{5}{4}π
\frac{3}{2}π
\frac{7}{4}π
x
-3
-2
-1
1
2
3
y
15

Determine the equation of the graphed function given that it is of the form \\ y = - \sin \left(x - c\right) - d, where c is the least positive value and x is in radians.

-1π
-\frac{5}{6}π
-\frac{2}{3}π
-\frac{1}{2}π
-\frac{1}{3}π
-\frac{1}{6}π
\frac{1}{6}π
\frac{1}{3}π
\frac{1}{2}π
\frac{2}{3}π
\frac{5}{6}π
x
-4
-3
-2
-1
1
y
16

Determine the equation of the graphed function given that it is of the form \\ y = - \cos \left(x + c\right) - d, where c is the least positive value and x is in radians.

-1π
-\frac{3}{4}π
-\frac{1}{2}π
-\frac{1}{4}π
\frac{1}{4}π
\frac{1}{2}π
\frac{3}{4}π
\frac{5}{4}π
\frac{3}{2}π
\frac{7}{4}π
x
-3
-2
-1
1
y
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U34.AoS1.13

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